Compare function pointers against 0 rather than nil.
diff --git a/src/cmd/9660/dump9660.c b/src/cmd/9660/dump9660.c
index 95bba37..b66e364 100644
--- a/src/cmd/9660/dump9660.c
+++ b/src/cmd/9660/dump9660.c
@@ -146,7 +146,7 @@
 	/*
 	 * Read new files into memory
 	 */
-	if(rdproto(proto, src, addprotofile, nil, &iroot) < 0)
+	if(rdproto(proto, src, addprotofile, 0, &iroot) < 0)
 		sysfatal("rdproto: %r");
 
 	if(mk9660){